Adsorption Behavior and Reaction Properties of NO and CO on Ir(111) and Rh(111)

Adsorption and reactions of NO over the clean and CO-preadsorbed Ir(111) and Rh(111) surfaces were investigated using infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD). Two NO adsorption states, indicative of hollow and atop sites, were present on Ir(111). Only NO adsorbed on hollow sites dissociated to N_a and O_a. The dissociated N_a desorbed as N₂ by recombination of N_a and by a disproportionation reaction between atop-NO and N_a. Preadsorbed CO inhibited atop-NO, whereas hollow-NO was not affected. Adsorbed CO reacted with O_a and desorbed as CO₂. NO adsorbed on the fcc-hollow, atop, and hcp-hollow sites in that order over Rh(111). The hcp-NO was inhibited by preadsorbed atop-CO, and fcc-NO and atop-NO were inhibited by CO preadsorbed on each type of the sites, indicating that NO and CO competitively adsorbed on Rh(111). From the Rh(111) surface-coadsorbed NO and CO, N₂ was produced by fcc-NO dissociation, and CO₂ was formed by reaction of adsorbed CO with O_a from dissociated fcc-NO.